Firebird RDBMS offers ANSI SQL features & runs on Linux, Windows & several Unix platforms. Features excellent concurrency & performance & powerful stored procedure & trigger language.
More information and downloads at https://firebirdsql.org/, issue tracker is https://github.com/FirebirdSQL/firebird/issues
...Functionally equivalent to a simplified version of Microsoft Access. Written primarily in PHP using the MySQL database engine. Supports all platforms that PHP/MySQL supports: Linux, Unix, Windows.